Electrolytic cell



Oct. 14, 1958 R. H. COLEMAN ETAL 2,856,343

ELECTROLYTIC CELL Filed, Aug. 31. 1956 3 Sheets-Sheet 1 SR /9 VT W 4FIGURE ROBERT H.COLEMAN BEYMON BLANCHARD WAYNE J.JOK|LEHTO INVENTOR.

Bmgmdw Oct. 14, 1958 Filed Aug. 51, 1956 5 FIGURE u R. H. COLEMAN ET AL2,856,343

ELECTROLYTIC CELL 5 Sheets-Sheet 2 ROBERT H. COLEMAN BEYMON B LANCHAR DWAYNE J. JOKILEH TO INVENTOR.

Oct. 14, 1958 R. H. COLEMAN ETAL 2,856,343

ELECTROLYTIC CELL 5 Sheets-Sheet 3 Filed Aug. 31, 1956 ROBERT H. COLEMANBEYMON BLANCHARD WAYNE J. JOKI LEH TO INVENTOR.

BYMM

ELECTROLYTIC C-ELL Application August 31, 1956, Serial No. 607,473

7 Claims. Cl. 204-243) This invention relates to an improvedelectrolytic cell for fused salt electrolysis and, more particularly, tocells adapted for electrolysis of a molten salt to produce an alkalimetal. Still more particularly, the invention relates to such cells,adapted for electrolysis of a fused salt such as sodium chloride underconditions to produce sodium, of improved construction and designwhereby during operation of the cell damage to the anode or anodes issubstantially prevented or obviated and the sidewall support and bottomseal structure are considerably strengthened and improved to preventbath leakage from the cell.

In certain types of modern electrolytic cells for electrolysis of fusedsalts, disadvantages are encountered as, by reason of temperaturegradients that occur, thermal stresses are set up that result incompression in theb'ase portion of the cell whereby fracturing of theanodes (e. g., graphite) occurs. In illustration, certain cells ofmodern type comprise a horizontally disposed base plate having ananode-receiving socket in which an anode is vertically placed and whichextends into an electrolysis zone. At the periphery of the base plate,an upstanding flange is attached perpendicular to the plane of the baseplate. Between this flange and the shell, which has a smaller diameterthan the base plate, there is an annular space which is filled with arefractory insulating seal. Additionally, such cells are provided with alayer of refractory, insulating cement covering the base plate and of athickness suflicient to completely surround and tightly embrace theanode or anodes at a height above the anode-receiving socket or sockets.Although cells of such design are normally adequate, they are subject toobjection in that, during operation, expansion of components of the cellbase structure occur. Since the forces that result therefrom are opposedby the flange at the periphery of the base plate, to which the flange isrigidly attached as by welding, compressive forces are created whichcause crushing of the graphite anode disposed in the anode-receivingsocket in the base plate. Obviously, occurrence of anode fracturing isobjectionable as it results in a high voltage drop across the cell whichlowers power efflciency, disturbs the thermal balance, and eventuallynecessitates pumping out and complete rebuilding of the cell. Suchpremature pumping, before the cell has served a useful life, results inserious loss of sodium production and materially increases operatingcosts.

Moreover, in cells as aforedescribed other disadvantages are encounteredfor the following reasons:

(1) The insulating refractory joint directly under the steel shellbetween bricks which serve as points of support for the shell is veryweak and therefore easily penetrated by the molten electrolyte.

(2) An uneven foundation is provided for the sidewall bricks since in"the construction of the cell the first course of bricks must be laid onan intermediate layer of the refractory cement bottom material. A secondsealing layer of this same refractory insulating cement Unitfd Statestent must then be poured after these bricks are in position. Thisweakens the bottom structure of the cell since the bond between the twolayers of refractory cement as well as the bond between the partiallydried refractory cement and brick are inherently of lower strength andtherefore subject to rapid penetration by the molten electrolyte.

(3) Moreover, in those cells wherein the top surface of the refractoryinsulating seal in the space between the shell and flange is at a levelsubstantially higher than the layer of refractory material covering thebase plate, the additional height of insulating refractory materialretains the heat energy at the base of the cell and sufficient basecooling is therefore not obtained which again promotes seepage of moltenelectrolyte through the refractory in the cell bottom.

Such penetration of the bottom refractory and lower sidewalls by thecell bath is extremely detrimental to cell operation since shortcircuits develop through the penetrated portion of the refractorywhereby the steel shell on the sidewall of the cell no longer remainselectrically neutral, and becomes anodic. In addition, a further hazardmay result due to seepage of the molten electrolyte from the cell to thecopper bus bars located beneath or to personnel working underneath.

It is the primary object of this invention to provide an electrolysiscell of improved construction to obviate or substantially minimizeobjectionable features of electrolysis cells as aforedescribed. It isstill another object of this invention to provide a fused saltelectrolysis cell of improved construction to prevent undesiredfracturing of anodes during operation of the cell. It is still a furtherobject of this invention to provide a fused salt electrolysis cell ofimproved design whereby, in addition to prevention of fracturing of theanode or anodes, improved cell bottom and sidewall construction areobtained thereby preventing undesired seepage of cell bath through thelower portion of the cell. These and other advantages that result fromthe improved electrolytic cell embodied herein will be apparent from thefollowing more detailed description thereof.

Generally speaking, the fused salt electrolysis cell comprises a metalbase plate insulated from ground, an anode-receiving socket set in saidbase plate, an anode (e. g., graphite) set in said socket and extendinginto the electrolysis zone of said cell, a layer of refractory,insulating material covering said base plate of a thickness sufiicientto surround and embrace said anode at a height above said socket, cellside walls constructed of a refractory-lined metal shell, the bottomportion of said side walls being spaced from said base plate, a metalcathode located in the electrolysis zone and an electrical connectionextending through a side wall of said cell, a flange attached to saidbase plate extending upwardly to a height above the bottom of said cellandspaced away from said shell, a refractory insulating seal in thespace between said shell and flange, and a compressible heat resistantmaterial in between the lower inner wall portion of said flange andrefractory material in the space between said shell and flange.

In a specific embodiment, a fused salt electrolysis cell as embodiedherein comprises a horizontally disposed steel base plate forming thecell bottom and insulated from ground, said plate extending laterallybeyond the side walls and spaced below the lower edge of the shell ashereinafter described, an anode receiving socket formed in the said baseplate in which a graphite anode is disposed to extend upwardly to theelectrolysis zone, a layer of refractory insulating material coveringthe base plate and extending upward to completely surround and tightlyembrace said 'anode at a height above said socket, cell side walls of adiameter smaller than the base plate and consisting of a steel shell,compressible heat resistant innerlining material and refractory brickwall reposing on a complete mortared course of refractory bricks laid onthe said base plate, an upstanding steel flange, spaced from andconcentric with the shell, at the periphery of the base plate, saidflange extending upward above the bottom edge of the shell to a heightno higher than thelevel of the top surface of the refractory materialthat covers the anode sockets and forms the cell bottom lining, and alayer of compressible heat resistant dielectrical material separatingsaid flange from the shell and side wall supporting refractory bricks.In the electrolysis zone a steel cathode supported by arms extendingthrough the side walls for electrical connections is disposed in amanner to completely surround the anode in conventional manner.

In order to more fully describe the invention, reference is made to theaccompanying drawings which, in Fig. I, partly in vertical section andpartly in elevation, shows an embodiment of the invention with Fig. IIbeing an exploded view of the lower left hand portion of Fig. l; andFig. III being an alternate embodiment of the invention over that shownin Fig. II. In all of the figures, the same reference numerals have beenused to designate similar elements. It should be understood, however,that such embodiments have been utilized for purposes of illustrationand not limitation.

In the drawings, in which Fig. I and II, illustrate the lower portion ofa fused salt electrolytic cell, there is shown a cell cylindrical inshape having a centrally located vertical, graphite anode 2 surroundedby an annular steel cathode 3 which is supported by two arms 4. Theanode is supported by base plate 5 which is a circular steel platehorizontally placed and having therein a socket 6 for the anode. At itsperiphery, plate 5 is provided with an upstanding flange 7. Plate 5 isinsulated from ground by insulators 24 and is supported by beams 25.Anode 2 is centered in socket 6 by any suitable means such as theprojection 8 on the interior bottom wall of socket 6 and set screws 9.

The side walls of the cell are formed first of a cylindrical steel shell10 which is open at top and bottom and provided with two openings forcathode arms 4. The diameter of shell 10 is smaller than that of plate 5so that when the shell and anode are concentrically placed there is anannular space between shell 10 and flange 7. A complete row of mortarjoined refractory bricks 11 is laid on plate 5 to support shell 10 andrefractory brick lining 15, and a layer of compressible, thermallystable,

dielectrical material 12, such as asbestos, is placed upon the inside ofsaid shell 10, in between the shell and the refractory lining. Betweenflange 7 and the shell support brick 11, a layer 13 of compressible,thermally stable, dielectrical material is installed to a height notsubstantially greater than that of the shell support brick. Arefractory, insulating cement 14 is then placed in the annular spacebetween the upstanding flange 7 and shell 10. Compressive layer 13 mustnot extend substantially higher than support brick 11, since upstandingflange 7 must exert retaining force on refractory seal cement 14 andshell 10.

On the inside of the cell, after the first upright course of side wallbrick 15 is laid, the layer of refractory cement 14 may be poured andrammed tight, in one single operation, in sufficient thickness to coverthe top of the anode socket 6. Following this operation, shell 10 linedwith compressible material 12 as shown, may be bricked up in theconventional manner with suitable refractory brick 15. During thebricking operation, cathode 3 is installed. In order to expedite theinstallation, with the cathode arms 4 projecting through the sides ofthe cell, shell 10 is preferably formed in two halves which aresubsequently fastened by conventional means, such as flanges 16 andbolts 17 after the cathodes are in place.

Cathode arms 4 are sealed by refractory insulating cement 18, held inplace by flanges 19 or other suitable means. The cell may be completedby installing the remaining conventional elements (not shown) such as acollector ring and domesupport assembly, diaphragm, gas collecting dome,riser pipe and the like in the usual manner, none of these being a partof this invention. Electrical connections are made in the usual manner,for example, to anode 2 by means of bus bars 20 and bolts 21 and tocathode arms 4 by bus bars 22 and bolts 23.

If desired, the cell may be provided with cooling means, and forexample, by providing a cooling jacket for anode socket 6.

The distance between flange 7 and shell 10 may be varied considerablybut the distance in combination with the thickness of refractoryinsulating cement and compressible refractory material 13 must be suchthat plate 5 is electrically insulated from shell 10.

The height of flange 7 and the insulating seal therein are kept atsubstantially the same or lower level than the top of refractory cement14 such that suficient cooling of cell bath occurs to decrease seepageof molten salt electrolyte through the refractory lining 15 of shell 10in the lower portion of the cell.

The compressible, thermally stable, preferably dielectrical material,such as compressible material 13 and, compressible material 12, shouldbe resistant to temperatures of at least 300 C. Such compressiblematerials may suitably consist of asbestos in the form of mats orsheets, molded forms of asbestos, mica bonded to asbestos, quartz paper,ceramic paper or other suitable thermally and preferably electricallyresistant materials having a, physical form which permits a substantialdegree of compression. Layers of such compressible materials having atotal thickness of approximately 4; to inches have been found to besuitable, depending on the compressibility of the particular materialused and the coefi'icient of expansion of the refractory cement.

The present invention provides a means for absorbing and neutralizingthe stresses imposed upon shell 10 and flange 7 by reason of expansionof plate 5 and refractory cement 14 during ope-ration of the cell. Ithas been found that, in the absence of use of such a compressiblematerial in the manner disclosed herein, the thermal stresses areeventually translated to compressive forces acting upon anode 2 causingthe latter to break resulting in a considerable decrease in powerefliciency of the cell, dangerous bath leakage through the bottom andeventual premature pump-out of the cell. Moreover, the improvement ofthe seal directly under the shell, the improved foundation provided forthe sidewall brick, the more uniform, non-stratified single pouring ofthe refractory cement bottom and the additional cooling provided by thelowered flange height all contribute to more positive, controlledsealing of the bath within the cell.

In Figure III a still further embodiment is shown which incorporates thesame principles of construction in an alternate way. In this case, shell10 has been offset at the bottom by welding a continuous formed angle tothe lower periphery of the shell 10 which rests on support brick 11. Thefirst course of sidewall brick is laid on the offset angle of the shellagainst insulating and compressive material 12, compressive anddielectrical material 13 is placed against the inside of the angle andthen the refractory cement bottom 14 is poured in one continuous layer.

Although, in the specific embodiment utilized for illustrative purposesa cell of circular construction has been employed, other modes ofconstruction may be used inpossible to produce still other embodimentswithout departing from the inventive concept herein disclosed, and it isdesired therefore that only such limitations be imposed on the appendedclaims as are stated therein.

What is claimed is:

1. A fused salt electrolysis cell comprising a horizontally disposedmetal base plate, an anode-receiving socket set in said plate andextending below the bottom thereof, an anode set in said socket andextending upward into a zone of electrolysis, a metal cathode in saidzone surrounding said anode, a refractory-lined metal shell having asmaller cross-section than said plate, said cathode being supported insaid zone by cathode-supporting means extending through an opening insaid metal shell, the lower edge of said shell being spaced above thetop of said plate and supported by a refractory material support forsaid shell on said plate, a refractory material covering said base plateand extending upward to completely surround and tightly embrace saidanode at a height above said socket, an upstanding flange at theperiphery of said base plate and extending above the bottom of saidshell, a refractory insulating seal in the annular space between saidflange and lower part of said shell and a compressible heat-resistantmaterial in between the inner side wall of said flange and therefractory material support for said shell, said compressibleheat-resistant material being more compressible than said refractoryinsulating seal in the annular space between said flange and lower partof said shell.

2. A cell, as defined in claim 1, wherein the compressibleheat-resistant material is disposed in between the inner wall of saidflange at a portion thereof not substantially above the refractorysupport for said shell.

3. A cell, as defined in claim 1, wherein the refractory insulating sealin the annular space between said flange and lower part of said shellfills said annular space to a height not substantially higher than theupper surface of the refractory covering the base plate and surroundingthe anode.

4. A fused salt electrolysis cell comprising .a horizontally disposedsubstantially circular metal base plate, an anode-receiving socket setin said plate and extending below the bottom thereof, an anode set insaid socket and extending upward into a zone of electrolysis, a metalcathode in said zone surrounding said anode, a refractory lined metalshell having a smaller diameter than said plate, said cathode beingsupported in said Zone by cathode-supporting means extending through anopening in said shell, the lower edge of said shell being spaced abovethe top of said plate and supported by refractory brick disposed inbetween said plate and said lower edge of said shell, a refractorymaterial covering said plate and extending upward to completely surroundand tightly embrace said anode at a height above said socket, an upstanding flange at the periphery of said plate and extending above thebottom of said shell, a refractory insulating seal in the annular spacebetween said flange and lower part of said shell, and a compressibleheat-resistant material disposed in between the inner side wall of saidflange and the refractory brick support for said shell, saidcompressible heat-resistant material being more compressible than saidrefractory insulating seal in the annular space between said flange andlower part of said shell.

5. A cell, as defined in claim 4, in which a compressible heat-resistantmaterial lining is disposed in the inner wall surface of said shell inbetween said shell and the refractory lining for said shell.

6. A cell, as defined in claim 4, in which the lower edge of the shellis supported by a complete mortared course of refractory brick.

7. An electrolysis cell, as defined in claim. 1, wherein thecompressible heat-resistant material is asbestos.

References Cited in the file of this patent UNITED STATES PATENTS

1. A FUSED SALT ELECTROLYSIS CELL COMPRISING A HORIZONTALLY DISPOSEDMETAL BASE PLATE, AN ANODE-RECEIVING SOCKET SET IN SAID PLATE ANDEXTENDING BELOW THE BOTTOM THEREOF, AN ANODE SET IN SAID SOCKET ANDEXTENDING UPWARD INTO A ZONE OF ELECTROLYSIS, A METAL CATHODE IN SAIDZONE SURROUNDING SAID ANODE, A REFRACTORY-LINED METAL SHELL HAVING ASMALLER CROSS-SECTION THAN SAID PLATE, SAID CATHODE BEING SUPPORTED INSAID ZONE BY CATHODE-SUPPORTING MEANS EXTENDING THROUGH AN OPENING INSAID METAL SHELL, THE LOWER EDGE OF SAID SHELL BEING SPACED ABOVE THETOP OF SAID PLATE AND SUPPORTED BY A REFRACTORY MATERIAL SUPPORT FORSAID SHELL ON SAID PLATE, A REFRACTORY MATERIAL CONVERING SAID BASEPLATE AND EXTENDING UPWARD TO COMPLETELY SURROUND AND TIGHTLY EMBRACESAID ANODE AT A HEIGHT ABOVE SAID SOCKET, AN UPSTANDING FLANGE AT THEPERIPHERY OF SAID BASE AND EXTENDING ABOVE THE BOTTOM OF SAID